No one gets to decide who you are except you. Period. No one gets to tell you how capable you are or who you can become. People will undoubtedly talk and give their opinions like they know something you don’t. And some people will not believe in you simply because they view the world from a lens of impossible.
But it’s you who gets to decide who to believe. You can believe the discouraging teacher or the pessimistic friend, or you can believe the little voice inside you that knows you are made for more, the voice inside you that believes in you & pushes you further.